The use of capacitive readouts in micro-electromechanical system (MEMS) sensors is susceptible to a variety of error mechanisms such as electrical feed-through, electrical damping of sensor mechanical modes, glass charging, work function changes of metallic capacitive plates, etc. In addition, the scale factor (SF) of the sensor, or the amount of signal you get out divided by the input signal, is directly related to sensitivity of the readout mechanism. These two factors limit the effectiveness of capacitive readout in MEMS sensors. Optical evanescent coupling is a promising readout technique that is potentially more sensitive than its capacitive counterpart and is not vulnerable to the electrostatic error mechanisms mentioned above. However, many of the proposed methods are not rugged enough to handle the harsh environmental factors that sensors are often exposed to. Further, while optical coupling has high sensitivity to measuring the vertical displacement of the silicon features, it is sometimes important or desirable to also measure horizontal motion.
For the reasons stated above and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the specification, there is a need in the art for alternate systems and methods of time-based optical pickoffs for MEMS sensors.